Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $43.85   9.178%   $47.8746   $47.87   $47.85   $47.90  
  Purchase #2 $225.87   6.676%   $240.9491   $240.95   $240.95   $240.90  
  Purchase #3 $150.55   3.151%   $155.2938   $155.29   $155.30   $155.30  
  Purchase #4 $61.69   9.270%   $67.4087   $67.41   $67.40   $67.40  
  Purchase #5 $167.75   3.670%   $173.9064   $173.91   $173.90   $173.90  
  Purchase #6 $124.90   13.337%   $141.5579   $141.56   $141.55   $141.60  
  Purchase #7 $220.37   4.684%   $230.6921   $230.69   $230.70   $230.70  
  7 purchase totals = $994.98       $1,057.6826   $1,057.68   $1,057.65   $1,057.70